Nowadays, the semiconductor manufacturing industry has rapidly developed under the Moore's law. It is required to increasingly elevate the performance and integration density of the integrated circuits and to decrease the power consumption as much as possible. To fabricate a short channel device with high performance and low power consumption will be a focus of the future semiconductor manufacturing industry. After entering into a technology node of 22 nm, the conventional planar field effect transistors may have increased leakage current due to the more and more severed short channel effect, and thereby cannot meet the development of semiconductor fabrication. In order to overcome the above issues, a multi-gate structure device has gained wide concerns, since the multi-gate structure device has excellent gate-control capability and transferring characteristic, and can increase a driving current density in a unit area while suppressing the short channel effect.
Although the multi-gate structure device has outstanding gate-control capability due to its special geometric construction, it may still have a large leakage current when its channel size shrinks to a certain degree, which may seriously affect the power consumption of the device. An SOI substrate can be used to decrease the leakage current. However, since the SOI substrate has a high cost and is distinct from the conventional bulk silicon, it is rarely used in the fabrication of large scale integrated circuits.